diag: Fix non-hdlc encoding of packets sent to remote proc

Raw packets received from userspace intended for remote proc ends
up discarded due to invalid handling of packets and leading to
non-hdlc mode never enabled on remote proc. Add missing non-hdlc
encoding of packets and handle raw packets properly to enable
non-hdlc mode on remote proc.

Change-Id: I12d9b00ffe62b498395d50355f763a201dc4adde
Signed-off-by: Manoj Prabhu B <bmanoj@codeaurora.org>